Freeze limiting absorption refrigeration machine

ABSTRACT

An absorption refrigeration system utilizing chilled water as a heat exchange medium. The system includes a chiller which provides reduced heat exchange area upon a drop in ambient air temperature by selectively block water flow paths between the chiller coils by the formation of ice to prevent complete freezeup of the chiller.

United States Patent John T. Fisher Indianapolis, Ind. 735,380

June 7, 1968 May 25, 1971 Carrier Corporation Syracuse, N.Y.

Inventor Appl. No. Filed Patented Assignee FREEZE LIMITING ABSORPTIONREFRIGERATION MACHINE 2 Claims, 5 Drawing Figs.

U.S. Cl

62/118,62/389, 62/399, 165/1, 165/117, 165/134 Int. Cl ..F25b 15/04,

Field of Search References Cited UNITED STATES PATENTS 2,056,970 10/1936Leopold Primary Examiner-Meyer Perlin Assistant Examiner-P. D. FergusonAttorneys-Herman Seid and Harry G. Martin, Jr.

ABSTRACT: An absorption refrigeration system utilizing chilled water asa heat exchange medium. The system includes a chiller which providesreduced heat exchange area upon a drop in ambient air temperature byselectively block water flow paths between the chiller coils by theformation of ice to prevent complete freezeup of the chiller.

Patented May 25, 1971 2 Sheets-Sheet l (I) 00 00 00 OD OO 0000 INVENTOR.

JOHN T. FISHER.

ATTORNEY.

Patented May 25, 1971 2 Sheets-Sheet 2 OOOOOOOOOOO OOOOOOOOOAWOOOOOOOOOOOOOO m OOOOOOOOOOOO FIG. 2

FIG. 5

INVENTOR. T. FISHER.

ATTORNEY.

FREEZE LIMITING ABSORPTION GERATION MACIHNE BACKGROUND OF THE INVENTIONAbsorption refrigeration systems of the type with which this inventionis concerned generally include a chiller having an evaporator coilthrough which refrigerant is passed in heat exchange relation withliquid heat exchange medium distributed over the evaporator coil, themedium being cooled by heat exchange with, the refrigerant, therebyevaporating the refrigerant. The chilled heat exchange medium isforwarded to a heat exchanger in a remote location to satisfy a coolingload and is returned from the remote location to be recooled in thechiller. It is desirable to use water as the heat exchange medium due toits favorable heat transfer characteristics, low cost and availability.However, when ambient temperatures drop, the temperature of the waterchiller may drop below the freezing point of water. It is thereforedesirable to reduce the heat exchange surface of the evaporator coil forlimiting the ice buildup in the chiller to maintain circulation ofchilled water to the area being conditioned.

SUMMARY OF THE INVENTION This invention relates to an absorptionrefrigeration machine employing an improved chiller constructionincluding a double row evaporator coil adapted for refrigerant flowtherethrough, the coil i'ows being spaced to promote the formation ofice during low ambient temperature operating conditions so as to reducethe heat exchange area thereof. The coils are arranged to block the flowof heat exchange medium thereover in three steps. First, by blocking thevertical spaces between the coil turns in each row, second, by blockingthe area between the two coil rows, and third, by blocking the spacebetween the outer coil row and the chiller coil, thereby reducing theheat transfer surface area of the coil to the inner surface of the innercoil.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram ofan absorption refrigeration system employing the present invention;

FIG. 2 is a sectional view of the water chiller employed in therefrigeration system;

FIG. 3 is a sectional view of a portion of the chiller illustrating theformation of ice in the vertical spaces between the coil turns;

FIG. 4 is a sectional view similar to FIG. 3 showing a further formationof ice in the space between the two coil rows;

FIG. 5 is a sectional view similar to FIGS. 3 and 4 showing furtherformation of ice to block the flow of heat exchange medium over theoutside surface of the outer coilrow.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, there is shown a refrigeration system comprising a primaryabsorber 10, a condenser 11, an evaporator or chiller 12, a generator13, a solution-cooled absorber l4 and a iiquid-suction heat exchanger 15connected to provide refrigeration. A pump 16 is employed to circulateweak absorbent solution from primary absorber to generator 13. As usedherein the term weak absorbent solution" refers to a solution which isweak in absorbent power and the term strong absorbent solution refers toa solution which is strong in absorbent power. A suitable absorbentsolution for use in the system described is water and a suitablerefrigerant is ammonia.

Liquid refrigerant condensed in condenser 11 passes through refrigerantliqttid passage 18, and refrigerant restriction 20 to heat exchange tube22 of liquid-suction heat exchanger 15. The liquid refrigerant is cooledin tube 22 and emerges from the liquid-suction heat exchanger and passesthrough refrigerant restriction 24 into heat exchanger 26 in chiller 12.

A fluid medium such as water to be chilled passes over the exterior ofheat exchanger 26 where it is chilled by giving up heat to evaporaterefrigerant within the heat exchanger. The chilled medium passes out ofthe chiller 12 through line 28 to suitable remote heat exchangers (notshown) after which it is returned to the chiller through inlet 30 forrechilling.

The cold refrigerant evaporated in heat exchanger 26 passes throughrefrigerant vapor passage 32 and through liquid-suction heat exchanger15 in heat exchange relation with liquid refrigerant passing throughtube 22. The refrigerant vapor then passes through refrigerant vaporpassage 34 into solution-cooled absorber 14.

The solution-cooled absorber 14 is formed within a tubular orcylindrical vessel 38 by a tubular, preferably, cylindrical internalbaffle 36 which divides the tubular cylindrical vessel 38 into thesolution-cooled absorber l4 and a second solution chamber 40. Vessel 38is preferably closed at both ends. Baffle 36 may be provided with a topcover plate 37 having a plurality of vapor discharge apertures 42therein to allow vapor to escape from solution-cooled absorber 14 intochamber 40.

A weak solution heat exchanger 44, preferably comprising a helical coilis disposed within solution-cooled absorber 14. A plurality ofhorizontal plates 46 are secured to a central support 48 and arrangedwithin baffle 36 to cooperate with annular grooves 50 and heat exchanger44 to provide a tortuous path for passage of vapor and solution throughsolutioncooled absorber 14. Suitable packing such as Raschig rings 52may fill the space between the uppermost plate 46 and the top of thesolution-cooled absorber to reduce the tendency for solution froth toescape through discharge apertures 42.

A refrigerant vapor distributor header 54 is secured to close the bottomof baffle 36. Header 54 is provided with refrigerant vapor ports 56 forpassage of refrigerant vapor from line 34 into solution-cooled absorberl4 and chamber 40. Strong solution from generator 13 is supplied to thetop portion of solution-cooled absorber 14 through line 58. The strongsolution passes downwardly through the solution-cooled absorber incounterflow relation to upwardly passing refrigerant vapor and weaksolution passing through coil 44. A strong solution discharge passage 60is provided adjacent the lower portion of baffle 36 for passage ofsolution from the solution-cooled absorber into chamber 40.

Solution discharge passages 62 are provided for passing a mixture ofrefrigerant vapor and solution from chamber 40 to primary absorber 10.Each of the discharge passages comprises a tubular member having anupper open end for admission of vapor and a solution inlet aperture 64which is disposed below the level of absorbent solution in chamber 40.This insures a mixed flow of liquid and vapor to the primary absorber.

A cooling medium, preferably ambient air, is passed through the primaryabsorber 10 in heat exchange relation with the absorbent solution tocool the absorbent solution to promote the absorption of the refrigerantvapor in the absorber. The same cooling medium may be supplied tocondenser 11 in heat exchange relation with refrigerant therein tocondense the refrigerant.

Cold weak absorbent solution passes from primary absorber 10 throughline 66 into pump inlet tank 68. Weak solution from inlet tank 68 issupplied to weak solution pump 16 through line 72. Liquid from pump 16passes through pump discharge tank 74 to a rectifier heat exchange coil76. From coil 76, the weak solution passes through line 78 to weaksolution heat exchanger 44 in solution-cooled absorber 14. The weaksolution from coil 44 passes through line 80 into the upper portion ofgenerator 13 alongwith any vapor formed in coil 44.

Generator 13 comprises a shell 82 having fins 84 suitably affixedthereto as by welding. The generator is heated by a gas burner 86 orother suitable heating means. The weak solution is boiled in generator13 to concentrate the solution, thereby forming a strong solution andrefrigerant vapor.

The hot strong absorbent solution passes upwardly through the analyzersection of generator 13 through analyzer coil 88 in heat exchange withweak solution passing downwardly over the coil. The warm strong solutionthen passes through line 58 which has solution restrictor 87 therein andis discharged into the upper portion of solution-cooled absorber l4.

Refrigerant vapor formed in generator 13 passes upwardly through theanalyzer section thereof where it is concentrated by mass heat transferwith weak solution passing downwardly over analyzer coil 88. Analyzerplates 90 in generator 13 pro vide a tortuous path for flow of solutionand vapor to assure intimate contact therebetween to improve the massheat transfer. The refrigerant vapor from the analyzer section passesthrough reflux plate 92 in heat exchange relation with absorbentcondensed in rectifier 94. The vapor then passes through rectifier 94 inheat exchange relation with rectifier heat exchange coil 76. Absorbentcondensed in rectifier 94 flows downwardly onto plate 92 where it isheated by the refrigerant vapor passing therethrough. The heatedabsorbent is then passed to the generator along with the weak solutiondischarged into the generator from line 80. Refrigerant vapor passesfrom rectifier 94 through line 96 to condenser 11 to complete therefrigeration cycle.

The water chiller 12 as illustrated in FIG. 2 comprises an outercylindrical shell 102 having a top member 104 secured thereto. Acylindrical liner 106 is disposed within shell 102 in spaced relationthereto. A suitable insulating material 108 such as urethane foam isprovided between shell 102 and liner 106 and on the bottom of the liner.The insulation is preferably foamed in place to form a completeassembly. The double row, helically shaped tube-type heat exchange coil26 in chiller 12 is disposed within liner 106 for passage of refrigeranttherethrough. A distribution tray 110 which is disposed above coil 26receives water returned from the remote heat exchangers through returnwater line 30. Distribution tray 110 is provided with two concentricrows of downwardly directed nozzles 112 which are aligned above the tworows of coil 26 for discharge of water from tray 110 onto the coil. Acap 114 is suitably affixed to tray 110 to deflect the stream of waterfrom line downward into tray 110. Overflow towers 116 are provided ontray 110 to prevent an exces sive accumulation of water therein.

When outdoor ambient temperatures drop, the chiller temperature may dropto a level sufficient to cause freezing of the water being circulatedtherethrough. Unless this freezing is controlled, all of the water inthe chiller will freeze which will prevent flow of chilled water to theremote heat exchangers. To prevent complete freezeup of the chiller,applicant has provided a novel chiller heat exchanger configurationwhich assures selective freezing of the water in the chiller to reducethe heat transfer area of the heat exchanger to prevent completefreezeup of the chiller, thereby assuring sufficient water forcirculation to the remote heat exchangers irrespective of chillertemperature. FIG. 3 illustrates a first chiller condition wherein icehas formed in the vertical spaces between the coil turns of the heatexchanger. This reduces coil surface by the amount of the surfacecovered by the ice on the bottom and top of the individual coil turns.If this reduced heat exchange area is great enough to cause furtherfreezing of water in the chiller, ice will form in the space between thetwo concentric coil rows, This will reduce the heat exchange surface toinclude only the outer surface of the larger coil row and the innersurface of the smaller coil row. If this heat exchange surface is stillexcessive in relation to coil temperatures, further icing will occur asillustrated in FIG. 5 to block the passage of chilled water along theouter surface of the larger coil row. This effectively reduces the heatexchange area of the coil to the inner surface of the smaller coil row.Any further icing of the chiller would cause a greater blanket of ice tobe built up on the inside surface of the inner coil row. This ice willact as insulation to further reduce the heat transfer between the coiland the chilled water. As can be seen from FIG. 5, the iced chiller willhave a cylinder of ice surrounding the coil. After icing of the chilleras illustrated in FIG. 5 has occurred, there is still a sufiicientquantity of water in the chiller for circulation to the remote heatexchangers.

While I have described a preferred embodiment of my invention, it willbe understood that the invention is not limited thereto since it may beotherwise embodied within the scope of the following claims.

Iclaim: l. A method for varying the heat exchange between refrigerantand a heat exchange medium in an absorption refrigeration system chillerhaving a tube-type heat exchanger therein including the steps of:

reducing the heat exchange surface of the heat exchanger by formingrelatively small ice bridges in the vertical spaces between adjacenttubes of the heat exchanger to prevent flow of heat exchange mediumtherebetween;

further reducing the heat exchange surface of the heat exchanger byforming an ice bridge, larger than those between the vertical rows ofthe heat exchanger, between one row of heat exchanger tubes and a secondadjacent row to prevent flow of heat exchange medium therebetween; and

further reducing the heat exchange surface by forming an ice bridgelarger than that between adjacent rows of the heat exchanger between theheat exchanger tubes and the chiller wall to prevent flow of heatexchange medium therebetween.

2. An absorption refrigeration system comprising an absorber, agenerator, a condenser, and a chiller adapted to provide refrigeration,said chiller comprising:

a casing; and

a tube-type heat exchanger disposed in said casing adapted forrefrigerant flow therethrough, said heat exchanger comprising twoconcentric helically shaped tube rows, said rows being spaced from eachother a distance greater than the vertical spaces between said tubes andless than the space between the tube row and said casing so that upon adrop in temperature of the heat exchange medium, after initial formationof ice in the vertical spaces between the tubes, ice will form in thespace between the tube rows and thereafter form between the outer tuberow and said casing to permit flow of heat exchange medium only over theice coating on the inner surface of the inner tube row for heat transferbetween the refrigerant and the heat exchange medium.

1. A method for varying the heat exchange between refrigerant and a heatexchange medium in an absorption refrigeration system chiller having atube-type heat exchanger therein including the steps of: reducing theheat exchange surface of the heat exchanger by forming relatively smallice bridges in the vertical spaces between adjacent tubes of the heatexchanger to prevent flow of heat exchange medium therebetween; furtherreducing the heat exchange surface of the heat exchanger by forming anice bridge, larger than those between the vertical rows of the heatexchanger, between one row of heat exchanger tubes and a second adjacentrow to prevent flow of heat exchange medium therebetween; and furtherreducing the heat exchange surface by forming an ice bridge larger thanthat between adjacent rows of the heat exchanger between the heatexchanger tubes and the chiller wall to prevent flow of heat exchangemedium therebetween.
 2. An absorption refrigeration system comprising anabsorber, a generator, a condenser, and a chiller adapted to providerefrigeration, said chiller comprising: a casing; and a tube-type heatexchanger disposed in said casing adapted for refrigerant flowtherethrough, said heat exchanger comprising two concentric helicallyshaped tube rows, said rows being spaced from each other a distancegreater than the vertical spaces between said tubes and less than thespace between the tube row and said casing so that upon a drop intemperature of the heat exchange medium, after initial formation of icein the vertical spaces between the tubes, ice will form in the spacebetween the tube rows and thereafter form between the outer tube row andsaid casing to permit flow of heat exchange medium only over the icecoating on the inner surface of the inner tube row for heat transferbetween the refrigerant and the heat exchange medium.